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w 1, v DE K Re ELECTRICAL CONTROL SYSTEM FOR AUTOMATIC TELEPHONE SYSTEMSOriginal Filed Sept. 14, 1942 T Sheets-Sheet 1 INVENTOR.

' GERALD DEAKIN ATTORNEY Oct. 1, 1946. DEAKIN ELECTRICAL CONTROL SYSTEMFOR AUTOMATIC TELEPHONE SYSTEMS Original Filed Sept; 14, 1942 7Sheets-Sheet 2 P b m Dibbbbb bbbbbbb bbbbbbb r b 1 1 1 11111111111111111111 14 41 Q AA lull OH x INVE NTOR. G l RA LD DEAKINATTORNEY G. DEAKIN ELECTRICAL CONTROL SYSTEM FOR AUTOMATIC 'IELEPIIOIIESYSTEMS 7 Sheets-Sheet 3 Original Filed Sept. 14, 1942 K n W i .LNBHHOQSOONV INVENTOR- GERflLD DEAKIN BY ATTORNEY Oct. 1,1946. O G, DEAKIN Re22,794

ELECTRICAL CONTROL SYSTEM FOR AUTOMATIC TELEPHONE SYSTEMS Original FiledSept. 14. 1942 -7 Sheets-Sheet 4 IN V EN TOR. GERALD DEAKIN i/1TB BY Yi- ATTORNEY SE LECTOR REGISTER Oct 1946. G. DEAKIN Re 22,794

I ELECTRICAL CONTROL SYSTEM FOR AUTOMATIC TELEPHONE SYSTEMS I OriginalFiled Sept. 14, 1942 7 Sheets-Sheet 5 Lily;

INVENTCR. Y GERALD DEAKIN AVE RAGE POTENTIAL-E) AVERAG E POTENTIAL Ex -5ATTORNEY ELECT RI CAL CONTROL SYSTEM FORAUTOMATIG TELEPHONE SYSTEMS oriinai Filed Sept. 14, 1942 7 Sheets-She t s IN V EN TOR.

- GERALD DEAKIN ATTORNEY Oct. -1, 1946. G. DEAKIN Re 22,794

I ELECTRICAL CONTROL SYSTEM FOR AUTOMATIC TELEPHONE SYSTEMS OriginalFile d Sept. 14, 1942 'v sheets-shee't 7 IN VEN TOR. GERALD DEAKINATTORNEY Reissued Oct. 1, 1946 ELECTRICAL CONTROL SYSTEM FOR AUTOMATICTELEPHONE SYSTEMS Gerald Deakin, New York, N. Y., assignor toInternational Standard Electric Corporation, New York, N. Y., acorporation of Delaware Original No. 2,351,016, dated June 13, 1944,Serial No. 458,297, September 14,- 1942.

Application for reissue April 23, 1945, Serial No. 589,819

31 Claims.

This invention relate to electrical control systems of the kind adaptedfor the control of switching apparatus in telecommunication systems,remote control systems and the like, and for the selective operation ofother apparatus such as electric elevators, gun control, calculatingmachines, telegraph printers, or ticket printers.

One object of the invention is the provision of a control circuit whichis adapted to respond instantaneously to a desired potential or range ofpotentials.

Another object of the invention is the provision of a control circuitwhich will effectively and instantaneously arrest the movement of anoperating mechanism such as a selector switch, or which will actuate aselected one of a number of operating mechanisms, responsive to theapplication of a predetermined potential to a control circuit orconductor.

A still further object is the provision of a control circuit forcontrolling the operation of selector switches in a telecommunicationsystem in which the lines or groups of lines accessible to a selectorswitch are distinguished by characteristic and different direct currentpotentials, whilst afiording the facility that a, switch will be causedto hunt continuously until a wanted line or an idle line of a wantedgroup of lines becomes available.

These and other objects of the invention will be clear from aconsideration of the following description taken in conjunction with theaccompanying drawings in which,

Fig. 1 is a circuit diagram illustrating an application of my inventionto the selective control of an operating mechanism,

Fig. 2 is a further embodiment of my invention in which a threeelectrode gas tube is used,

Fig. 3 shows a modification of part of the circuit of Fig. 1, Fig. 2,

Fig. 4 are tube characteristics referred to in the description,

Fig. 5 is a modification showing how my invention may be employed forthe instantaneous selective actuation of any one or more of a pluralityof controls, and e Fig. 6 shows how my invention may be applied to thecontrol of selector switches in a telecommunication system.

7 Figs. 7 and 8 show further embodiments of my invention.

Fig. 1 shows the fundamental control circuit according to my invention,which consists of a twin triode vacuum tube V and a cold cathode gastube GV having two control electrodes CEI and (IE2 constituting anauxiliary gap and two main gap electrodes G and H. The positive terminalof a high tension battery HTB is connected to one of the main gapelectrodes H of tube GV over a switch SW2 and over load resistances RIand R2, respectively, to the anodes Al and A2 of the tube V. The upperends of the resistances RI and R2 are respectively connected to theauxiliary gap control electrodes CEI and CE2 of the gas tube GV. Theresistances R1, R2, are all of the order of 50,000 to 100,000 ohmsdepending upon the high tension voltage used and the characteristics oftube V. It will be seen that the positive potentials on the controlelectrodes CE! and CEZ are normally the same and thus there is notendency for the tube GV to ionize.

The object of the circuit is to permit the placing of a plurality ofpairs of potentials on the control grids GI and G2, respectively, of thetube V in such manner that for each pair of potentials there is acritical potential for the cathode C which when realized, and only whenrealized, will cause a much greater flow of current through resistanceRI than through resistance R2 or vice versa, thereby lowering thepotential of CEI with respect to CE2 to the breakdown voltage of thecontrol gap which in certain gas tubes now in use is in the neighborhoodof volts. When any other potential, either positive or negative anddifiering from the critical potential by more than a certain minimumamount determined by the tube characteristics, is applied to the cathodeC, the currents through resistances RI and R2, respectively remainsufiiciently close together to prevent a breakdown potential fromdeveloping across the auxiliary gap CEI, 0E2 of the gas tube GV.

In Fig. 1 there is shown diagrammatically means for applying differentselected potentials from battery BI to the control grids GI and G2,respectively, over resistances R4 and R5. Potentiometers or tappingpoints between storage cells may equally well be used. The cathode C oftube V is connected to a brush B which is arranged to wipe over a numberof terminals I to H1 under the control of an operating mechanism OM. Theterminals I to Ill represent a plurality of selections, operations orcontrols of any desired kind. They may, for example, represent variousoperations which it is desired to control e. g. from a remote point,such as the control of switching operations, calculating machines,ticket printers, industrial controls, etc. A distinctive potentialtapped from a potentiometer connected across a battery B2 or takendirectly from the battery is applied to each terminal I to I0, thepotentials increasing in steps of say 4 volts. It is not necessary,however, that the potentials of the terminals are in regular ascendingorder. The same battery or other source of potential may be used for BIand B2.

A control relay or contactor REL is connected to the main gap electrodeG and is thus in the main gap circuit. The armature of relay REL in itsoperated position opens the circuit of the operating mechanism OM.

The switch SVVI is adapted to close the circuit of the operatingmechanism OM. The function of the switch SW2 is to open the main gapcir: cuit to deionize the gas tube GV'after the desired selection hasbeen effected. The switch SW2 may be actuated automatically under thecontrol for example of another relay controlled by relay REL.

In the arrangement illustrated, the tubV is chosen to have such acharacteristic that only when the approximate potential of GI is 2 voltswith respect to cathode C and the approximate potential of G2 is 4 voltswith respect to C is the. difference between the anode currents of thetwo discharge paths suflicient to develop a voltage between the controlelectrode CEI and E2 of the gas tube GV which will ionize this tube.When the grids GI- and G2 becom more negative, the difference betweenthe respective anode currents is insuiiicient to develop a breakdownvoltage between CEI and CE2 and when both grids are very negative noanode current will flow through either tube. When both grids GI and G2are positive with respect to the cathode approximately the same currentsflow through the two discharge paths since the grid resistances R4 andR5 which are of the order of 100,000 ohm depending upon the batteryvoltage and tube characteristics; maintain both the grids atsubstantially zero potential, this being due to the action of gridcurrent which appears as soon as the grid tends to go positive.

Assume now, for example, that it is desired to effect a desiredselective operation by stopping the brush 3 on terminal 5 which isconnected to -14 volts. Grid GI is arbitrarily connected to a '16 voltstapping on battery BI and grid G2 to a -l -8 volt tapping on thisbattery. Switch SWI is closed manually or automatically to complete thecircuit of the operatin mechanism OM which advances the brush 13 overthe contacts I to In. The switch SW2 is also closed to connect the hightension battery HTB to th main gap electrode H.

When brush B engages terminal I which is connected to 2 volts, thepotential of grid GI is 14 volts and that of grid G2 16 volt relative tothe cathode C. As already explained, substantially, no current flowsthrough either discharge path and the gas tube GV will not fire. In thesecond position, on terminal 2, zero potential is applied to cathode C,this position being assumed to be inactive. Thus the potential of GI is16 volts and G2 is 18 volts and again no current fiows over eitherdischarge path. On terminal 3 the respective potentials of GI and G2 arevolts and +8 volts relative to the cathode, and on terminal 4, 10voltsand 12 volts, and in neither position will the gastube GV fire. Inposition 5 the potential on GI is 2 volts and that on G2 is 4 volts.These are the critical voltages previously mentioned which cause aconsiderable current to flow through RI but not through R2 whereby abreakdown voltage 'is de- 4 veloped across the auxiliary gap CE1.CE2 andthe gas tube GV fires. When the auxiliary or control gap is ionized, themain gap GH also ionizes instantly and energizes relay REL which opensits back contact and opens the circuit of the operating mechanism OM.

It will be appreciated that any double tube having suitablecharacteristics may be used for the tube V. Thus double tetrodes ordouble pentodes may be employed instead of double triodes. Two separatetubes may, of course, be employed instead of the double tubeillustrated, and in fact the pentode RCA SSH? with a high tensionbattery of 'volts has been found to operate satisfactorily. 1 7

It is also understood that the current in the main gap circuit of thegas tube GV may be used in any convenient manner to control theoperating mechanism. A potential developed across a load resistor may,for example, be used as the starting voltage of a Thyratron which isarranged to control the operating mechanism.

The operating mechanism OM may be arranged to advance a slider over thepotentiometer across battery B2 so that when a potential which matchesthe potentials on grids GI and G2 is reached the gas tube will fire andstop the operating mechanism.

The characteristics of the tube V may be chosen to provide any requireddegree of tolerance in regard to the critical voltages which must bepresent between the respective control grids and the cathode of thistube in order to cause the gas tub'eGV to fire. When, for example,storage batteries are use'd as the source of potential it may bearranged that the gas tube will fire'when the voltage of grid GIrelative to the cathode is between 1.8 and 2.3 and that of the grid G2relative to the cathode is between 3.6 and 4.6. In other applications,however, the critical voltages may be required to be held withinnarrower or broader limits.

Fig. 2 "shows a modification of Fig. l in which the twin'triode V ofFig. 1 is replaced by two pentodes VI and V2 and the four-electrode gastube'GV is replaced by a three electrode gas tube GVI. In thisarrangement it is necessary to employ a separate high tension batteryHTBI for the main discharge path C, H of the gas 'tube GVI. As in thecircuit of Fi 1 when the critical potentials which match the potentialon brush B are applied to the 'control grids of tubes VI and V2, or viceversa, currents of sufficiently different magnitudes flow in theanode-cathode circuits 'of the tubes VI, V2to develop a potentialdifferent at the upper ends of the load resistors RI and R2 great enoughto fire the auxiliary'gap CG. The tube 'GVI is thereby ionized, the maingap CH strikes and the relay REL is energized.

Instead of employing, as in Fig. 1, a twin tube V, the two halves ofwhich have similar characteristics, or, as in Fig. 2, two separate tubesVI and V2 having similar characteristics, together with means forapplying predetermined critical potentials to the respective controlelectrodes thereof, two tubes VI, V2, Fig. 3, may be employed havinginherently different characteristics, or alternatively there may be usedtwo similar tubes suitably biased to work on different points of theircharacteristics. In this arrangement it is only necessary to apply thesame critical potential to both control grids.

Fig. '4 shows in the full line curve the grid volts-anode currentcharacteristic of a suitable tiibewhi'chfnaybe'used if both tubes VI"and V2 of Fig. 3 are to have similar characteristics. With switch S inits lower position tube VI is unbiased, whereas the grid of V2 is biasedsay two volts negative by a small battery C. It will be noted that ifthe potential applied to both grids from battery BI is approximately twovolts more negative than the potential applied to both cathodes overbrush B, a large anode current flows through tube VI but only a verysmall anode current fiows through tube V2. The difference a in anodecurrent is sufficiently great to develop a firing potential across theauxiliary gap of the gas tube. It will be seen, however, from aninspection of the curve that for all other voltage differences betweenthe brush B and the tap on the battery BI, the difference in therespective anode currents is substantially less, and it can be arrangedthat the gas tube GV will not fire responsive to a potential differencedeveloped by such currents.

Instead of differently biasing the respective tubes VI and V2, the tubesmay be chosento have different characteristics. For example, one tubemay be chosen to have a characteristic as shown in the full line curveon Fig. 4 and the other a different characteristic, as shown in thedotted line curve. It will be appreciated from an inspection of thesecurves that when and only when a potential of approximately 2 volts withrespect to the cathodes is applied to both grids will there exist asubstantial difference between the anode currents in the two tubes. Inthis modification the grid bias battery C will be removed by the switchS.

It will be appreciated that instead of applying two diiferentpredetermined potentials to respective control electrodes of twodischarge paths from potential source BI and a common potential to thetwo cathodes (Fig. 2) or to a common cathode (Fig. 1) over brush B, thecommon potential may be applied to the two control electrodes inparallel and the two difierent potentials applied respectively to twoseparate cathodes.

In any of the modifications described, an electromagnetic relay may beemployed in place of the gas tube GV. In this case the relay winding maybe connected directly across the upper ends of the resistance RI, R2 soas to be energized responsive to the potential difference developedacross these points. Alternatively a relay might be provided havingdifferential windings replacing the resistances RI and R2 or connectedserially therewith. In this case the relay would operate only when thereis a considerable difference in the currents through the two windings,which would correspond to the case when the difference in the dropsthrough the resistances RIand R2 are sufllcient to operate the gastubeGV of Fig.1 or GVI of Fig. 2.

.As illustrated in Fig. 5, the invention may also be employed for theinstantaneous operation of any one or more of a plurality of controlsresponsive to the application of a predetermined potential to a singlecontrol conductor. An individual control circuit comprising a dualthermionic emission tube (VZ-Vn), and a gas tube (GVl-GVn) similar tothe circuit VGV of Fig. 1 is provided for each control, selected pairsof potentials EXlEYl-EXnEYn being applied in any suitable manner to therespective grid electrodes GI, G2 of each dual tube VlVn and thecathodes ClCn of all the tubes VZ-Vn being connected in multiple to acontrol conductor X. Relays MZ-Mn or other current or voltage responsivedevices are connected in the main gap circuits of the gas tubes GVZ--GVn. I.

It will be appreciated that when a selected potential (ElEn) is appliedin any desired manner to the control wire X and thus to the commoncathode circuit, only that thermionic emission tube (or tubes) therespective potentials (EX,EY) on the grids of which are matched to thisselected potential, will pass anode currents sufiiciently different inmagnitude to set up a voltage difference across the auxiliary gap of theassociated gas tube (GVl-GVn), large enough to fire the tube and causethe energization of the control relay (Ml-Mn) The control circuit of theinvention is particularly well adapted to the control of high speedselector switches in tele-communication systems. Fig. 6 illustrates oneway in which the control circuit of the invention may be adapted to thecontrol of a selector switch in an automatic telephone exchange system.Components in Fig. 6 similar to components in Fig. 1 are indicated bylike reference letters.

A battery of storage cells or potentiometers may be used to obtain thevarious D. C. poten tials. The use of storage cells, particularly thecells of the regular central ofiice 24 cell, 48 volt battery ispreferred. It is proposed to start, for example, with a potential EX ongrid GI, having a value of approximately 4 volts, that is, the averagepotential at the second cell of the exchange storage battery. Thisbattery has its positive pole grounded. The EX potential may vary duringthe operation of the exchange from 3.6 volts minimum to 4.6 voltsmaximum- A negative potential EY, always higher by the potential of onestorage cell, thus starting with an average of 6 volts, minimum 5.4volts maximum of 6.9 volts, is placed on grid G2. These are the firstpair of potentials. The remaining potentials up to I4 increase by stepsof 4 volts. Should the subscriber dial the digit 4, with the normalregister arrangement brush RBI will advance under control of powermagnet PR to the 4th terminal and will place potential EX ofapproximately 16 volts on grid GI and brush RB2 will place potential EYof approximately -18 volts on grid G2. When the register or othercontrolling device has placed a particular pair of potentials on gridsGI and G2, in the above mentioned case, 16 volts on GI and .18 volts onG2, the selector circuit is closed at a contact X in any known manner,for example by a relay energized after the commencement of dialling of adigit, thus closing the driving circuit of the selector from battery atthe back of relay GVR of the register through relay AR of the selectorto ground and over a front contact of relay AR through the selectorclutch magnet PS to ground. Brush T of the selector advances. It firsttests terminal I which has an average E potential of -2 volts. It thentests terminal 2 which has anaverage E potential of 10 volts. In thesethree cases both grids GI and G2 are sufficiently negative with respectto the cathode to prevent any appreciable current from flowing throughRI and R2 so that a breakdown potential is not developed across thecontrol gap of GV. When brush T reaches terminal 4 an average Epotential of -14 volts is placed on the cathode. C.

The characteristic of tube V is such that with the cathodeC at thispotential and the grid GI at -16 volts and grid G2 at -18 volts, a-considerable fiow of current takes place through RIbut not through R2,thus a ,breakdownpoe .75 tentialis developed and GV fires... When thecontrol gap is ionized, the main gap ionizes instantly and operatesrelay GVR which opens its back contact and releases relay -AR and theclutch of the selector, thereby causing brush T-to cometo rest'on'terminal 4.

Should terminal 4 be busy, the E potential will not be present and theterminal circuit will be either grounded or open, for example, by arelay in another selector which has engaged the outlet. In either casethe grids GI and G2 will be snfficiently negative with respect to C sothat no appreciable current will flow through RI or R2 gas tube and GVwill not fire.

As 'the system provides for continuous huntingat the group selectors, agroup selector will pass over the wanted group in case all trunks in itare busy and will test the groups beyond and then restart the test allover again. When brush T reaches the terminal beyond, in this caseterminal 5, it will find an average E potential of -l8 volts on theterminal. This will make grid GI positive by 2 volts with respect to Cand grid G2 will have the same potential as C. The characteristics of Vand its associated circuits are such that under these conditionsapproximately equal currents flowthrough RI and R2 and a breakdownpotential is not developed in GV. As T tests terminals still morenegative, approximately equal currents continue to flow through RI andR2, but a breakdown potential is not developed in GV.

It has been assumed that the desirable difference-in potential between Eand EX is approximately 2 volts, but it may be found desirable toincrease or decrease this difference to make the best use of thecharacteristics of the tube V so as to obtain the maximum difference incurrent through RI and R2 when the cathode reaches the criticalpotential.

' The operation of the combination of tubes V and GV is practicallyinstantaneous, thus the controlling factor in the speed of hunting isthe speed with which relay GVR may be made to open its back contact andthe speed with which PS may be made to release and stop the selector. Itis known that speeds as high as 120 terminals per second can be obtainedwithout overstepping and that safe speeds as high as 80 are practicable.By a safe speed is meant a speed under which the brushes will makecontact with their corresponding terminals with ample margin so as toeliminate all possibility of one or more brushes becoming disconnectedfrom their corresponding terminals.

In Fig. 6 relays AR and power magnet PSare energized inmultiple, thus arelatively heavy current flows over the a wire to the back contact ofrelay GVR. This connection provides for the maximum speed of release.However, a sufficiently quick release may possibly be made by connectingonly relay AR to the back contact of "relay GVR and operating powermagnet PS over a front contact of relay AR, the armature which would beconnected to battery. alternative relay AR must break its front contactbefore the power ma'gnet can release. With this second arrangement arelatively light current "flows over the selector contacts and the backcontact of relay GVR.

,In the further modification shown in Fig. 7 the'high tension batteryHTB is connected'over two differential windings of a 'tr'ansformerTR tothe respective anodes of the tube V." A third windingv of thetransformer 'IR is grounded at One end 'and'at th other "end isconnected to an 8' auxiliary electrode of a three-electrode gas tube at'GV and over a condenser C to ground. 1

When the potentials applied to the cathode over test 'brush T matchesthe potentials applied to the grids of tube. V a strong pulse of currentinduced in the third winding of transformer TR fires the auxiliary gapG, C, of the gas tube GV which 'ionizes and strikes its main gap G, H,thereby energizing the relay GVR.

Fig. 8 shows a circuit somewhat similar to Fig. '7 except'that thetransformer TR1 has a single primary winding; connected either directlyor through a condenser across two resistors RI and R2 which function toproduce a differential voltage drop' just as described in conjunctionwith Fig. 1 where the critical test voltage is applied at T thedifference in currents through resistors RI, R2. cause a voltage dropacross the primary of transformer TRi sufiicient to fire the gas tubeGV.7

Other application and embodiments coming within the scope of theinvention as defined in the appended claims will occur to those versedin the am.

What is claimed is:

1. An electrical control system comprising two current conducting meanshaving different voltage-current characteristics such that for apredetermined voltage applied to them the difference between themagnitudes of the currents flowing through them is amaximum and forvoltages either greater or less than saidpredetermined voltage the saidcurrent difference rapidly decreases, means for deriving from saidcurrents a potential difference dependent upon said current difference,a control means arranged to be actuated only .by a potential exceeding apredetermined value, and means for applying said potential "differenceto said control means.

2. An electrical control system comprising two current conducting meanshaving difierent nonlinearvoltage-current characteristics such that fora predetermined voltage applied to, them the difference between themagnitudes of the cur rents flowing through them is a maximum and forvoltages either greater or less than said predetermined'voltagethe saidcurrent difference rapidly decreases, means for deriving from saidcurrents apo'tential difference. dependent upon said ourrent'difference, --a control means arranged "to be actuated only byapotentialsexceeding a predetermined value, and means-for applying saidpotential difference to said control means;

3. An electrical control system comprising two current conductingmeans'having similar nonlinear voltage-current characteristics such thatfor two predetermined voltages applied respectively to said currentconducting means the differ-ence b'etween the currents flowing through'60 them is a maximum means-for'deriving from In this the currentsflowing through said conducting means potentials of a value dependentupon the difference in the magnitudes of said currents, a contro'lmeansresponsive over a rangeof potentials exceeding a potental approximatelyequal to the potential corresponding to said maximum current differenceand means for applying said potentials to said control means.

4'. An electrical control system comprising an 7 electron dischargemeans including two electron discharge 'paths each comprising an anode,a cathode and a control grid and each having different gridvoltage-anode current characteristics such that for apredetermined-voltage applied to the controlgrids relative to thecathodes the difierenoe between the magnitudes of the respective anodecurrents is a maximum and for voltages on either side of saidpredetermined voltage the said current difierence rapidly decreases,meansfor deriving from said currents a potential difierence dependentupon said current difference, a control means arranged to be actuatedonly by a potential exceeding a predetermined value, and means fOrapplying said last-mentioned potential difierence to said control means.

5. An electrical control system comprising electron discharge meansincluding first and second electron discharge paths each consisting ofat least an anode, a cathode and a control electrode, means for applyingpredetermined potentials to said control'electrodes of such values thatsmall variations thereof cause but little difference in the valuerelative to one another of the plate currents flowing in said two paths,means for adding to said potentials a. critical potentialof such valuethat currents of substantially diiierent magnitudes traverse the saidpaths, control means and means responsive to the difference in saidcurrents for operating said control means.

6. A system in accordance with claim 5, wherein said electron dischargepaths inherently have different characteristics and equal potentials areapplied to the control electrodes thereof.

'I. A system in accordance with claim 5, wherein said electron dischargepaths inherently have the same characteristics and the control electrodeof one path is provided with a fixed bias relative to that on thecontrol electrode or the other path. i

8. An electrical control system comprising elec- I tron discharge meansincluding first and second electron discharge paths each consisting ofat least an anode, a cathode and a third electrode, means for applyingpredetermined difierent potentials respectively to one of the electrodesof each of said first and second discharge paths, means for applying acritical potential to another of the electrodes included in each saiddischarge path of such value that currents of substantially differentmagnitudes traverse the said first and second paths, means for derivingfrom said last mentioned currents a potential difference, a controlmeans, and relay means responsive to said potential diilerence foractuating said control means.

9. An electrical control system comprising electron discharge meansincluding first and second electron discharge paths each consisting ofat least an anode, a cathode and a third-electrode, means for applying apotential to one of the electrodes of each of said first and seconddischarge paths, means for applying a critical potential to another ofthe electrodes included in each said discharge path of such value thatcurrents of substantially difierent magnitudes traverse the said firstand second paths, means for deriving from said last mentioned currents apotential difierence, a transformer, means for applying said potentialdifierence to the primary of said transformer and controlmeans'connected to the secondary of said transformer.

10. An electrical control system comprising electron discharge meansincluding first and second electron discharge paths, first and secondcircuits respectively including said first and second discharge paths,means for applying predetermined potentials to said paths of such valuethat currents of substantially difierent magnitudes traverse the saidfirst and second circuits a transformer comprising three windings two of1.0 said windings being differentially arrangedand respectively includedin said first and second circuits, control means, and means responsiveto a current of predetermined value through said third winding foractuating said control means;

11. An electrical control system according to claim 10, wherein saidcontrol means comprises a gas tube including an auxiliary gap and a maingap, means provided for deriving a, starting potential from the currentin said third winding for striking said auxiliary gap.

i 12.- An electrical control system comprising a plurality of terminals,means for applying a predetermined potential to at least one of saidterminals, a contacting means, and operating mechas nism for causingsaid contacting means to make contact successively with said terminals,a first electron discharge means including first and sec-. ond electrondischarge paths, each consisting of at least an anode, a cathode and acontrol electrode, a second electron discharge means comprising a gastube havingan auxiliary control gap and a main discharge gap, a firstcircuit including said first discharge patina second circuit includingsaid second discharge path, a control relay, athird circuit includingsaid main discharge gap and said control relay, means for applying predetermined different potentials respectively to one of the electrodesconstituting each said first and second dischargepaths', a connectionfrom said contacting means to'another of the electrodes constitutingsaid first and second discharge paths, means for deriving voltages fromsaid first and second circuits and for applying said voltages toelectrodes constituting said auxiliary control gap, a circuit forcontrolling said operating mechanism, and means under the control ofsaid control relay for opening and closing said last-mentioned circuit.

13. A control circuit according to claim 12, wherein said means forapplying predetermined different potentials to said respective controlelectrodes. includes a resistance of such value that when said controlelectrodes tend to acquire such positive potentials with respect to thecathodes that grid currents flow, the respective control-electrodes areboth maintained at substane tially zero potential.

14. An electrical control system comprising a gaseous discharge tubehaving a main discharge path comprising a first pair of electrodes andan auxiliary discharge path comprising a. pair of starting electrodes,two resistances connected in series between said electrodes lastmentioned and means for passing currents of different magnitudes througheachof said resistances to produce a voltage drop across said pair ofstarting electrodes sufiicient to fire the said tube.

15. An electrical control system comprising a first electron dischargemeans including first and second electron discharge paths eachconsisting of at least an anode, a cathode and a third electrode, asecond electron discharge means comprising a gas tube having anauxiliary control gap and a main discharge gap, a first circuitincluding said first discharge path, a second circuit including saidsecond discharge path, a third circuit including said main dischargegap, means for applying predetermined different potentials respectivelyto one of the electrodes of each of said first and second dischargepaths, means forapplying a critical potential to an other of theelectrodes of each of said discharge paths of such value that currentsof substantially difierent magnitudes traverse the said first and secondcircuits, means for deriving from said last-mentioned currents a.potential difference and for applying said potential difference acrosssaid auxiliary control gap whereby said gas tube is ionized and said gapis fired and current flows in said third circuit, a control means andmeans responsive to said current flow for actuating said control means.

16; An electrical control system comprising a thermionic emissionelectron discharge means including first and second electron dischargepaths each comprising at least an anode, a cathode and a controlelectrode, a gas tube having a first pair of electrodes forming a maindischarge gap and a. second pair of electrodes forming an auxiliarydischarge gap, a high tension source connected across the anode andcathode of each said discharge path and across said first pair ofelectrodes constituting said main discharge gap, 2. control relay in theexternal main discharge gap circuit, a, first load resistance in theexternal anode cathode circuit of said first e1ectr0n discharge path, asecond load resistance in the external anode cathode circuit of saidsecond electron discharge path, means for applying a potential developedacross said first load resistance to one of the electrodes forming saidauxiliary discharge gap and for applying a potential developed acrosssaid second load resistance to the other of said electrodes forming saidauxiliary gap, means for applying predetermined difierent potentials tothe said respective control electrodes with respect to said point offixed potential of such value that a breakdown potential is developedacross said auxiliary discharge gap whereby said gas tube is ionized andsaid control relay is energized.

17. An electrical control system comprising a thermionic emissionelectron discharge means including first and second electron dischargepaths each comprising an anode a cathode and a control electrode, a gastube having a first pair of lectrodes forming a main discharge gap and asecond pair of electrodes forming an auxiliary discharge gap, a hightension source connected across the anode and cathode of each saiddischarge path and across said first pair of electrodes constitutingsaid main discharge gap, control means, a circuit including said maindischarge gap, a first load resistance inv the external anode cathodecircuit of said first electron discharge path, a second load resistancein the external anode cathode of said second electron discharge path,means for applying a potential developed across said first loadresistance to one of the electrodes forming said auxiliary discharge gapand for applying a potential developed across said second loadresistance to the other of said electrodes forming said auxiliary gap,means for applying predetermined difierent potentials to the saidrespective control electrodes with respect to a point of fixedpotential, and means for applying a potential to said cathode withrespect to said point of fixed potential of such value that a breakdownpotential is developed across said auxiliary discharge gap whereby saidgas tube is ionized and a current flows in said main discharge gapcircuit and means responsive to said current flow for actuating saidcontrol means.

18. An electrical control system comprising a plurality of controlcircuits each including a first electron discharge means comprisingfirst and second electron discharge paths each consisting of at least ananode, a cathode and a third electrode, a second discharge meanscomprising a gas tube having an auxiliary control gap and a maindischarge gap, a first circuit including said first discharge path, asecond circuit including said second discharge path, a third circuitincluding said main discharge gap, control means responsive to currentflow in said third circuit, means for deriving a potential difierencefrom the currents flowing in said first and second circuits and forapplying said potential difierence across said auxiliary control gap,means for applying predetermined difierent pairs of potentialsrespectively to pairs of similar electrodes of each control circuit, aconductor connected in multiple to another of the electrodes of eachsaid electron discharge path of all said control circuits and means forapplying a predetermined critical potential to said conductor.

19. An electrical control system comprising a plurality'of terminals,means for applying a predetermined potential to at least one of saidterminals, a contacting means, an operating mechanism for causing saidcontacting means to make contact successively with said terminals, afirst electron discharge means including first and sec ond dischargepaths, each consisting of at least an anode, a cathode and a controlelectrode, a second electron discharge means comprising a gas tubehaving an auxiliary control gap and a main discharge gap, a firstcircuit including'said first discharge path, a second circuit includingsaid second discharge path, a third circuit including said maindischarge gap, control means electrically associated with said thirdcircuit, means for applying predetermined different potentialsrespectively to one of the electrodes constituting each said first andsecond discharge paths, a connection from said contacting means toanother of the electrodes constituting said first and second dischargepaths, means for deriving voltages from said first and second circuitsand for applying said voltages to electrodes constituting said auxiliarycontrol gap, a circuit for controlling said operating mechanism, andmeans under the control of said control means for opening and closingsaid last-mentioned circuit.

20. An electrical control system comprising a plurality of controlcircuits each including a first electron discharge means comprisingfirst and second electron discharge paths each consisting of at least ananode, a cathode and a control electrode, a second electron dischargemeans comprising a gas tube having an auxiliary control gap and a maindischarge gap, a first circuit including said first discharge path, asecond circuit including said second discharge path, a third circuitincluding said main discharge gap, control means responsive to currentflow in said third circuit, and means for deriving a potentialdifference from the currents flowing in said first and second circuitsand for applying said potential difference across said auxiliary controlgap, means for applying predetermined different pairs of potentialsrespectively to the pairs of said control electrodes of each controlcircuit, a conductor connected in multiple to the cathode of each saidelectron discharge path of all said control circuits and means forapplying a predetermined critical potential to said conductor.

21. An electrical control system comprising a plurality of controlcircuits each including a first electron discharge means comprisingfirst and second electron discharge paths, each consisting of at leastan anode, a cathode, and a control electrode, a second electrondischarge means comprising a gas tube having a first pair of electrodesforming an auxiliary control gap and a second pair of electrodes forminga main discharge gap, a first circuit including a load resistance andsaid first electron discharge path, a second circuitincluding a secondload resistance and said second electron discharge path, means forapplying a potential developed across said first load resistance to oneof the electrodes forming said auxiliary control gap and for applying apotential developed across said second load resistance to the other ofsaid electrodes forming said auxiliary control gap, a third circuitincluding said main discharge gap, and control means responsive tocurrent flowing in said third circuit, means for applying predetermineddifferent pairs of potentials respectively to the pairs of said controlelectrodes of each control circuit, a conductor connected in multiple tothe cathodes of each of said electron discharge path of all the controlcircuits and means for applying a predetermined critical potential tosaid conductor.

22. An electrical control system comprising a first electron dischargemeans including first and second electron discharge paths eachconsisting of at least an anode, a cathode and a third electrode, asecond electron discharge means comprising a gas tube having anauxiliary control gap and a main discharge gap, a first circuitincluding said first discharge path, a second circuit m including saidsecond discharge path, a control relay, a third circuit including saidmain discharge gap and said control relay, means for applyingpredetermined different potentials respectively to one of the electrodesconstituting each said first and second discharge paths, means forapplying a critical potential to another of the electrodes constitutingeach said discharge path of such value that currents of substantiallydiferent magnitudes traverse the said first and secand circuits, meansfor deriving from said lastmentioned currents a potential difierence andfor applying said potential difference across said auxiliary control gapwhereby said gas tube is ionized, said main gap is fired and saidcontrol relay is energized.

23. In a telecommunication system, a selector switch comprising aplurality of test-terminals, a brush, and a magnet for controlling themovement of said brush over said terminals, a control switch comprisingfirst and second sets of terminals, first and second brushes for saidcontrol switch and means for moving said first and second brushes inunison to make contact with any predetermined pair of terminals of saidfirst and second sets of terminals, means for applying predeterminedpotentials to said test terminals, means for applying predeterminedpotentials to the terminals of said first and second sets of terminalsof said control switch such that the potentials applied to therespective terminals of each set of terminals are difierent but thepotentials applied to each pair of termials adapted to be simultaneouslyengaged by said first and second brushes difier by substantially thesame amount, a first electron discharge means including first and secondelectron discharge paths each consisting of an anode, a cathode and acontrol electrode, a second electron discharge device comprising a gastube having an auxiliary gap and a main discharge gap, a first circuitincluding said first discharge path, a second circuit including saidsecond discharge path, a control relay, a third circuit including saidmain discharge gap and said control relay, a connection from saidtestwiper of said selector switch to the cathode of each said first andsecond discharge paths, connectionsextending from said firstand secondbrushes of said control switch respectively to the control electrodes insaid first and second discharge paths, means for deriving voltages fIOmsaid first and second circuits and for applying said voltages toelectrodes constituting said aux iliary control gap, and means actuatedby the operation of said control relay for controlling the energizationof said selector switch magnet.

24. In a switching system, a plurality of conductors, means formaintaining on each conductor a predetermined steady direct currentpotential, potential comparing means including a high impedance path, afirst connecting means for connecting a first conductor with said highimpedance path, a second means for connecting other conductors with saidhigh impedance path, and means in said comparing means and responsive tothe connection to the high impedance path and two conductors, one by thefirst and the other by the second connecting means, and whose potentialsbear a predetermined relationship to one another for controlling theoperation of said second connecting means.

25. The switching system according to claim 24 and in which said secondconnecting means connects one conductor after another with said highimpedance path and is stopped under the control of said comparing means.

26. The switching system according to claim 24, and in which theoperation of said second connecting means is started by said comparingmeans upon the operation of said first connecting means.

27. The switching system according to claim 24 and in which said highimpedance path comprises an electron discharge path within a, vacuumtube having two electrodes to which the first and second conductors areconnected.

28. The system according to claim 24, and in which said high impedancepath is between the electrodes of a vacuum tube having a cathode, ananode and a grid, one of the connecting means being connected with thegrid and the other with the cathode, and the last mentioned means forcontrolling said second connecting means being connected with the anode.

29. The system according to claim 24, and in which said comparing meanscomprises a plurality of electron discharge paths whose number isindependent of the number of predetermined potentials.

30. In a switching system, a selector switch having a plurality ofterminal contacts and a contact wiper, control means for successivelyestablishing contact between said wiper and said terminals, means formaintaining on each said terminal a predetermined steady direct currentpotential, potential comparing means comprising an electron dischargepath, means for applying to said potential comparing means a selectedone of said predetermined potentials, a connection from said wiper tosaid comparing means, means including said potential comparing means andresponsive to the potential difference applied thereto for actuatingsaid control means to establish connection between said wiper and aterminal contact to which is applied a potential which bears apredetermined potential relationship to said selected potential.

31. In a, switching system a selector switch having a plurality ofcontacts and a contact wiper, control means for moving said wiper to 15SHQQessively establish contact between said wiper and said contacts, aplurality of sources of gliflerent steady direct current potential,means for applying to each said contact a predetermined steady directcurrent potential, potential comparing means having two terminals, meansfor connecting one of said last mentioned terminals to a selected one ofsaid potential sources and the other to said wiper, means under thecontrol of 16 said comparing means for actuating said control means to.arrest said Wiper when said selected potential and the potential derivedover said wiper are of the same polarity and substantially the samemagnitude, and means for preventing the actuation of said control meanswhen said selected potential is greater or less than the potentialderived over said wiper.

GERALD DEAKIN.

